The relative hardness of a mineral can best be tested by
a) scratching the mineral across a glass plate
b. squeezing the mineral with calibrated pliers
c. determining the density of the mineral
d. breaking the mineral with a hammer

Ais useful when you need a simple machine to you separate two things. a. lever b. screw c. pulley d. wedge

If the work required to stretch a spring 3 ft beyond its natural length is 15 ft-lb, how much work is needed to stretch it 27 in. beyond its natural length?

Aparticle's position is given by x = 3.00 - 9.00t + 3t2, in which x is in meters and t is in seconds. (a) what is its velocity at t = 1 s? (b) is it moving in the positive or negative direction of x just then? (c) what is its speed just then? (d) is the speed increasing or decreasing just then? (try answering the next two questions without further calculation.) (e) is there ever an instant when the velocity is zero? if so, give the time t; if not, answer "0". (f) is there a time after t = 3 s when the particle is moving in the negative direction of x? if so, give the time t; if not, answer "0".